Air pollution: An important risk factor for cardiovascular disease

Robert D. Brook, MD, is a professor of internal medicine at the University of Michigan. Photo courtesy American Heart Association

This month, APHA’s Year of Climate Change and Health is looking at air quality and climate change. Our guest blogger explores the cardiovascular health impacts of air pollution exposure in climate change in today’s post. Robert D. Brook, MD, is a cardiovascular medicine specialist and professor of medicine at the University of Michigan’s Division of Cardiovascular Medicine. A pioneering researcher in the field of environmental cardiology, Dr. Brook focuses on how air pollutants cause heart disease and trigger cardiovascular events. For more on this topic, tune in to Climate Changes Health: The Breath and Heart of It All, the fourth in our Year of Climate Change and Health webinar series on Monday, May 22 from 1:30-3 p.m.

Cardiovascular disease, or CVD, is our nation’s No. 1 killer and most costly chronic disease. In 2016 alone, CVD cost the United States $555 billion and is expected to cost the U.S. $1.1 trillion by 2035.

CVD is often thought of as a disease that solely affects the heart and blood vessels. But that couldn’t be further from the truth. In fact, repercussions from CVD can impact your brain, your heart, your lungs, your arteries and many other important organs. Likewise, an issue like air pollution — seemingly tied exclusively to pulmonary health — can actually have a measurable impact on a person’s overall cardiovascular health. In 2004 and again in 2010, an American Heart Association scientific statement concluded that short-term exposure — hours to days — to particulate matter, or PM, can contribute to acute cardiovascular morbidity and mortality such as heart attacks and strokes, while long-term exposure can even shorten life expectancy.

There is evidence that exposure to PM in the air can be associated with higher markers of inflammation throughout the body. Several studies indicate that exposure to PM is capable of impairing vascular function, particularly among higher-risk individuals and after traffic-related exposure. The major source of PM in the world, which is smaller than 2.5 microns, is created through human combustion of fossil fuels such as emissions from industry, traffic and power generation. Since PM is a product of burning fossil fuels, it is exceedingly common that U.S. citizens are exposed due to the high volume of motor vehicle travel in the U.S.: the average U.S. citizen over 15 years old spends 55 minutes per day travelling in motor vehicles.

The specific health consequences related to this type of PM vary based on length of exposure, locality, weather conditions, prior risk factors, etc. A person’s overall mortality risk increases on average by about 10 percent due to long-term PM exposure, and cardiovascular mortality appears to be elevated to a similar extent. Acute morbidity and mortality associated with PM exposure is principally seen among susceptible individuals such as the elderly, those with preexisting coronary artery disease and perhaps those with diabetes. Some studies have suggested that women and obese individuals may also be at higher risk, a troubling development due to the growing prevalence of obesity and diabetes in the United States.

However, correlations have been found between PM and several forms of CVD with or without prior risk factors. For instance, a Worcester Heart Attack study found an association between long-term exposure to traffic-related air pollution and heart attacks. Associations have also been found between elevated PM exposure and heart failure, arrhythmia and strokes. Some researchers have reported that instances of elevated smog in Los Angeles have led to increases in hospitalizations and deaths.

PM is not only concerning because it can trigger CVD instances in those already predisposed, but also because it could increase the risk of developing CVD risk factors, like high blood pressure and diabetes. This elevates air pollution as yet another important risk factor for cardiovascular disease, in addition to obesity, diabetes, physical inactivity, poor nutrition, smoking and others.

As a result, it is important for those already predisposed to or living with CVD to understand the impact of air quality on their health, and to take the proper precautions. Based on an individual’s level of risk, it may be prudent to monitor the Environmental Protection Agency’s Air Quality Index to reduce exposure. Federal recommendations advise that “people with heart or lung disease, older adults and children should avoid prolonged or heavy exertion. All others should reduce prolonged or heavy exertion when pollution levels are high.” However, because individuals cannot avoid or control exposure to PM, it is crucial that we work together to lower the amount of human-created PM and pollution to protect the cardiovascular health of our population.